libecap3-dev binary package in Ubuntu Xenial amd64

 eCAP is a software interface that allows a network application,
 such as an HTTP proxy or an ICAP server, to outsource content
 analysis and adaptation to a loadable module. For each applicable
 protocol message being processed, an eCAP-enabled host application
 supplies the message details to the adaptation module and gets
 back an adapted message, a "not interested" response, or a "block
 this message now!" instruction. These exchanges often include
 message bodies.

Source package